Turn your computer off and turn it back on. See if the video comes back. If it doesn't then try another known working monitor on the computer. If you get video with the 2nd monitor then that means the original monitor is bad. If you still don't get video with the 2nd monitor then that means there is an issue with the CPU because you have no video output.

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Hit the space bar or enter key to wake it up. Maybe you have to pres the Power Button to wake it up.

Read the manual to see how to wake it up.

Get online
and got to www.google.com In the google search box type: "Dell
Support" (without the quotes and put your manufacturer name before Support).
Look for downloads and drivers. Enter your model number and operating
system when requested. Look for Manuals on the site and search them on hibernation.

Below is what your manual says to get out of hibernation you have to press the Power Button (very last paragraph at bottom).

Hibernate Mode
Hibernate mode conserves power by copying system data to a reserved area on
the hard drive and then completely turning off the computer. When the computer
exits hibernate mode, it returns to the same operating state it was in before
entering hibernate mode.NOTICE: You cannot remove
devices or undock your computer while your computer is in hibernate
mode.
Your computer enters hibernate mode if the battery charge level becomes
critically low.
To manually enter hibernate mode:

Press
<Fn><F1>.

or

Click the Start button, click Turn off computer, press and
hold <Shift>, and then click Hibernate.

or

Depending on how you set the power management options on the Advanced
tab in the Power Options Properties window, use one of the following
methods to enter hibernate mode:

Press the power button.

Close the display.

Press <Fn><Esc>.

NOTE: Some PC Cards may not
operate correctly after the computer exits hibernate mode. Remove and reinsert the card, or simply restart
(reboot) your computer.To exit hibernate mode, press the power button. The computer may take a short
time to exit hibernate mode. You cannot make the computer exit hibernate mode by
pressing a key or touching the touch pad or track stick. For more information on
hibernate mode, see the documentation that came with your operating system.

It probably going into "Hibernation" mode.
Try turning off or disabling the "Hbernation"
how to do this can easily be found by going to your "Help" menu... type in "Hibernation" and follow the instructions.

Turn Hibernate off for one thing. Hibernation leads to registry problems and boot issues. Go to control panel > power options > hibernate tab > uncheck the box. Reboot the machine. If you want, the laptop will go into standby mode after a period of time and will wake up with a touch on the touchpad. Go back to power options and there are settings in there that you can tailor to your liking.

Hibernate mode is a power saving feature for computers. In hibernate
mode, the current state of a computer is saved to the hard disk, and
the computer shuts down. A user will have to power on the computer to
restore the previous settings. When a computer resumes from hibernate
mode, it reads the saved settings from the disk and restores the system
state as it was before it entered hibernate mode. By default, hibernate
mode is disabled. If a computer is not ACPI-enabled or APM-enabled,
users will have to enter hibernate mode manually. Users cannot set the
computer to automatically hibernate after a certain time. With
ACPI-enabled and APM-enabled computers, users are able to set hibernate
mode automatically

How to enable Hibernate:Please follow this steps below to enable your Hibernate features:

1. Go to Main screen in your windows then right click your mouse to an empty area in your main menu.2. After clicking the right click please select the properties then go to Screen Saver Tab.3. Please Click the Button name Power then click the Hibernate Tab.4. Please check the CheckBox name Enable Hibernation to enabled the hibernation if it is not hibernated.5. To try test the Hibernate process please follow the steps in How to start using Hibernate below.

How to start Using Hibernate:Please follow this steps below to active your Hibernate Features:

Make sure all necessary programs are closed prior to shutting down.
Hibernating will put all programs to "sleep," but some programs won't
start up properly. Experiment after this to figure out which programs
perform as intended.

Click Start and Shut Down,

Point the standby button and maintain the shift key pushed,

A new hibernation button appears: click it while still holding the shift key: voila your PC will hibernate.

Sounds like you may of put the Laptop into Sleep or Hibernation Mode. If you have a User Manual for your Machine, then have a look on how to Activate/Deactivate Sleep/Hibernation Mode, as it's usually a combination of keys. If you have not got a manual, then let me know the Model Number of your Macjhine and I'll get it for you :-).